The present invention relates to medical imaging systems in general, and in particular, to ultrasound imaging systems.
In many clinical applications, a physician or ultrasound sonographer is interested in viewing more than one type of ultrasound data at a time. This is particularly true when diagnosing arterial diseases where the physician wishes to view the structure of a patient""s vessel and the velocity or volume of blood flowing through it.
One dual imaging mode is referred to as BD mode, wherein the ultrasound system produces a two-dimensional greyscale image of the tissue structure beneath the ultrasound transducer as well as a spectral Doppler graph showing velocity of moving blood flow at a position in the body defined by a range gate.
A common problem encountered during BD mode imaging occurs when a vessel being viewed moves with the cardiac cycle or due to patient breathing. With the vessel moving, the user has to continually reposition the range gate over the vessel in order to capture the Doppler data of the blood flowing within the vessel. Moving the range gate can be particularly cumbersome for cardiac vessels which are generally small and tend to move relatively large distances with each cardiac cycle.
Given this problem associated with conventional dual mode imaging, there is a need for a mechanism that can automatically track the position of a vessel as it moves with the cardiac cycle or with movement of the patient and can reposition the range gate over the vessel without user intervention.
The present invention is a method for automatically positioning a range gate over a moving vessel for use in capturing ultrasound data. A sequence of Doppler pulses is applied to a patient and an average velocity of the tissue is determined at a number of depths. A search is performed to locate the depth having the greatest velocity. The range gate is then placed at the depth associated with the greatest velocity.
In a currently preferred embodiment of the invention, the average velocity at each depth is determined using an MC imaging mode that calculates the first lag autocorrelations of the Doppler data received from the sequence of Doppler pulses. The results of the autocorrelation calculations may be interpolated to locate a depth having a peak mean velocity over which the range gate is placed. Preferably, the MC imaging calculations are performed in the background and do not interfere with the normal display data being produced by the ultrasound imaging system